1. Field of the Invention
The present invention relates to an endoscope apparatus that controls various imaging modes thereof and its control method.
2. Description of the Related Art
An endoscope apparatus is used to diagnose the condition of the body cavity of a patient, such as the esophagus, stomach and large intestine, by using images (image diagnosis, which is diagnosis by observing images of the body cavity of the patient or the like). The endoscope apparatus obtains images of the body cavity of the patient by a scope inserted into the body cavity. In recent years, when diagnosis is performed by using images obtained by the endoscope, endoscopic images obtained by the scope of the endoscope are displayed on a monitor in real time. A doctor performs image diagnosis while looking at the monitor. Therefore, the doctor can diagnose the patient while recognizing the positions of the images displayed on the monitor. Meanwhile, observation modes using endoscopes include an ordinary observation mode, a fluorescent observation mode, and a narrow-band mode to help doctors easily perform image diagnosis. The ordinary observation mode observes a subject when white light is output to the subject. The fluorescent observation mode observes fluorescence output from the subject when the subject is illuminated with fluorescence. The narrow-band mode observes the subject when the subject is illuminated with narrow-band light.
Automatic switching of the various observation modes has been proposed so that doctors can perform efficient image diagnosis (for example, please refer to Japanese Unexamined Patent Publication No. 2007-020728 (Patent Literature 1)). Patent Literature 1 proposes automatically switching imaging modes among the ordinary observation mode, the narrow-band observation mode, and the fluorescent observation mode based on the magnification of a lens.
Further, automatic switching of the magnification of an imaging lens attached to the leading end of a scope based on the various imaging modes has been proposed (for example, please refer to U.S. Pat. No. 6,582,362 (Patent Literature 2)). Patent Literature 2 utilizes the tendency that when AEC (automatic exposure control) for controlling the diaphragm (aperture stop) of a light source unit to maintain the lightness of the image at a constant level is performed, if a distance to an object (subject) changes, the state of the diaphragm changes. In Patent Literature 2, the distance to the object is recognized based on the state of the diaphragm, and judgment is made, based on the distance, as to whether close-up imaging or distant-view imaging has been performed. If it is judged that close-up imaging has been performed, the high-frequency component of the obtained image is enhanced. If it is judged that distant-view imaging has been performed, the low-frequency component of the obtained image is enhanced.
Besides the case proposed in Patent Literature 2, which measures the distance between the scope and the subject by using AEC, automatic switching of close-up imaging and distant-view imaging based on the region to be imaged is desired to perform efficient image diagnosis.